JP2003151749A - Induction heater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heater providing a small load vibration and requiring a reduced high frequency current. SOLUTION: This induction heater has at least one heating section comprising a smoothing means 13 for smoothing an inverter power and at least one heating section not comprising the smoothing means 13 respectively. Maximum output of the heating section comprising the smoothing means 13 is smaller than that of the heating section not comprising the smoothing means 13. Thereby, reduction of the load vibration and the high frequency current can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating device used in general homes, restaurants, offices, factories and the like.

[0002]

2. Description of the Related Art A conventional method for heating an induction heating apparatus will be described with reference to FIGS. 6 and 7, taking an induction heating cooker as an example.

In the figure, 1 is a heating coil, 2 is an inverter circuit for supplying a high-frequency current to the heating coil 1, 3 is a load (object to be heated) that is induction-heated by a high-frequency magnetic field generated from the heating coil 1, and 4 is a commercial product. Power source, 5 is commercial power source 4
A rectifying bridge for rectifying the alternating current supplied from, 6 is a low-pass filter.

The voltage supplied to the inverter circuit 2 is a pulsating current having a frequency that is twice the commercial frequency, as shown in FIG. The capacity of the capacitor that constitutes the low-pass filter 6 is several μF to several tens of μF, and is not intended for commercial frequency smoothing (for example, several hundreds μF). In general, the power supplied to a motor drive inverter or lighting inverter is supplied in a form that is sufficiently smoothed against the commercial frequency in order to reduce humming noises and flicker. Was not smoothed. The main reason is that the load 3 is an object (material having a relatively heavy weight such as a pot) that is relatively insensitive to fluctuations in the commercial frequency.

When the material 3 made of a magnetic material is used, the load 3 to be induction-heated works in such a manner that the repulsive force and the attractive force have a phase difference. In the case of a non-magnetic material, no attractive force is generated and only repulsive force is generated. This increases as the power supplied to the load 3 increases.

[0006]

However, such a conventional induction heating device has the following problems.
That is, as described above, since the repulsive force or the attractive force acts on the load 3 at a cycle twice as high as the commercial frequency, the load 3 may be vibrated as a result.
The vibration of the load 3 may be the load itself or the vibration of the apparatus, which may give a user discomfort, or may deteriorate the performance of the apparatus in the case of a fixing device using induction heating such as a copying machine.

This problem is more remarkable when the load 3 is a non-magnetic material rather than a magnetic material (because only repulsive force is exerted). Furthermore, even with a non-magnetic material, the same volume has a relatively large weight and a low electrical conductivity. This is more noticeable in materials such as aluminum, copper, and titanium, which have the same volume and a smaller weight and higher electric conductivity than materials such as SUS304. In particular, in the case of a material such as aluminum having a small weight and a high electric conductivity, it is necessary to increase the amount of the magnetic field generated when an electric power similar to that of the magnetic body is supplied, so that the vibration of the load 3 becomes large and a large vibration occurs. There was a problem that sound was generated.

Against this background, in recent years, various configurations have been proposed for smoothing the inverter power supply even in the induction heating device, and further, the power factor reduction (harmonic current Improvement methods have also been proposed. However, in the induction heating device having the power factor improving means (harmonic current reducing means) necessary for smoothing the inverter power source, the rated power should be increased regardless of the material of the load. However, there is a problem that the harmonic current value inevitably increases. In other words, this problem is such that even when a magnetic pot such as an iron pot, which originally does not require a countermeasure against load vibration, is heated, the higher the rated power, the higher the harmonic current.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a comfortable and high-performance induction heating apparatus in which the vibration of the load is small and does not increase the harmonic current generated by the equipment. is there.

[0010]

In order to achieve the above object, the induction heating apparatus of the present invention comprises a heating section equipped with an inverter power supply smoothing means and a heating section not equipped with an inverter power supply smoothing means. Have at least one or more,
Further, the maximum output of the heating section having the smoothing means of the inverter power supply is made smaller than the maximum output of the heating section having the smoothing means.

As a result, it is possible to realize an induction heating device which reduces the vibration of the load while reducing the harmonic current.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 has at least one heating section equipped with a smoothing means for an inverter power supply and at least one heating section not equipped with a smoothing means for an inverter power supply. The maximum output of the heating unit equipped with the smoothing means is set smaller than the maximum output of the heating unit equipped with the smoothing means of the inverter power supply. Since the section does not have smoothing means, the harmonic current is reduced and in the heating section equipped with smoothing means,
Load vibration can be reduced.

According to a second aspect of the present invention, the input power at the time of heating a non-magnetic material load having a low electric conductivity in the heating section provided with the smoothing means is changed when the load of the heating section not provided with the smoothing means is heated. The induction heating device according to claim 1, wherein the induction heating device is smaller than the input power.
With an input power of about kW, since the heating section that has a large input power when heating a non-magnetic material load having a low electric conductivity, in which the load vibration due to the repulsive force is relatively small, is provided on the side without the smoothing means, It is possible to reduce the harmonic current.

According to the third aspect of the present invention, the non-magnetic material load is non-magnetic stainless steel. The induction heating device according to the second aspect provides a load resistance of 70 μΩ · cm. Since the value is about the same value, the repulsive force of the load is small and the harmonic current can be reduced.

According to a fourth aspect of the present invention, the input electric power at the time of heating a non-magnetic material load having a high electric conductivity in the heating section provided with the smoothing means is supplied to the heating section having no smoothing means at the time of heating the load. The induction heating device according to claim 1, wherein the load is larger than the input power, so that the non-magnetic material load and the high electrical conductivity material require a large amount of magnetic flux for heating, Although the vibration becomes even larger, the load vibration can be reduced because the heating section is on the side having the smoothing means.

According to a fifth aspect of the present invention, the induction heating device according to the second or fourth aspect is characterized in that the thickness of the portion of the load facing the heating portion is set to approximately 1 mm or more. Since the heating of the load having the thickness suitable for induction heating (that is, the skin resistance is an appropriate value) is performed by the heating unit on the side including the smoothing unit, it is possible to reduce the load vibration.

According to the sixth aspect of the invention, the load is repulsed by the induction heating device according to the second or fourth aspect, wherein the size of the load is set to substantially cover the heating portion. Since the load having a sufficiently large force is heated by the heating unit on the side provided with the smoothing means, the load vibration can be reduced.

According to the invention described in claim 7, the non-magnetic material load is a load made of an aluminum material. By using the induction heating device according to claim 4, the repulsive force becomes extremely large. Since the aluminum load is heated by the heating section on the side provided with the smoothing means, it is possible to significantly reduce the load vibration.

The invention according to claim 8 is characterized in that the non-magnetic material load is an aluminum material or a copper material, and the input power of the copper material is smaller than that of the aluminum material. By using the device, the copper load, which has a larger repulsive force than aluminum, is heated by the heating part on the side with smoothing means, and the input power is smaller than that of aluminum, so load vibration It is possible to reduce.

According to a ninth aspect of the present invention, the function of controlling the load to the set temperature based on the temperature detection of the load by the temperature detecting means is provided in the heating section having the smoothing means. By using the induction heating device according to any one of 1 to 8, heating having a temperature detection function is performed by a heating unit equipped with a smoothing means, so that load vibration is reduced and induction with better result detection performance is achieved. It serves as a heating device.

[0021]

EXAMPLES Examples of the present invention will be described below with reference to FIGS.
Will be described with reference to.

In FIG. 1, 10 is a commercial power source, 11 is a rectifying element for rectifying the commercial power source 10, and 12 is a power factor improving means, specifically, a passive filter configuration for suppressing harmonic current. Reference numeral 13 is a smoothing means, specifically, an electrolytic capacitor is used to prevent the drop of ripples generated in the cycle of the commercial frequency. Reference numeral 14 is an inverter to which the voltage smoothed by the smoothing means 13 is supplied. Generates high frequency current and loads 1
5 is configured to supply a high frequency magnetic field.

FIG. 2 shows an induction heating cooker as an example. The heating part 17 is a heating part equipped with the smoothing means 13 shown in FIG. 1, and is the maximum when heating the load 15 of iron-based material. The output is 2 kW. The heating unit 18 has the circuit shown in the conventional example (that is, the smoothing means 24 is not provided), and the maximum output when heating the load 15 is 3 kW. The heating unit 19 is a heating unit using a radiant heater. The heating units 17 to 19 are properly used according to heating and cooking.

FIG. 3 shows the waveform of the voltage applied to the inverter 14, and FIG. 3A shows the waveform of the voltage applied to the inverter of the heating section 18. As shown in the figure, the cycle in which the commercial frequency is full-wave rectified (8.3 ms at 60 Hz in the figure)
The non-smoothed voltage of is supplied. FIG. 3B shows a voltage waveform applied to the inverter of the heating unit 17, and as shown in FIG.
It is smoothed by the smoothing means 13. This smoothing makes it possible to reduce the vibration of the load 15 that occurs at a frequency twice the commercial frequency. The larger the capacity of the smoothing means 13, the smaller the ripple of this voltage, and the vibration of the load 15 can be further reduced.

In the heating section 17 equipped with the smoothing means 13, basically, the input current becomes large and the power factor deteriorates (that is, the harmonic current is large) near the peak voltage of the commercial power source 10. However, in the case of this embodiment. , Smoothing means 1 for the heating part that maximizes the maximum output
Since the heating unit 18 is not provided with 3, the problem can be reduced, and a comfortable induction heating device in which the load 15 vibrates less in the heating unit 17 can be realized.

In the case of the present embodiment, the maximum output is ensured in the case of a load of a magnetic substance such as iron (that is, the input power to a load of a non-magnetic substance such as non-magnetic substance stainless steel is applied to a magnetic substance such as iron). The loss of the inverter, the loss of the heating coil, etc. is larger than the input power, so that it is small.) In this respect, the load vibration is not a problem even without the smoothing means 13.

In the case of the present embodiment, when the load 15 is a non-magnetic load and is made of non-magnetic stainless steel having a low electric conductivity, the input power in the heating section 18 is 2.5 kW and the input power in the heating section 17 is 1.6 kW. I am trying.

The shape of the load 15 is as shown in FIG.
The heating coil 16 almost covers the heating coil 16.
The thickness of the portion facing 6 is set to approximately 1 mm or more.

When the load 15 is a non-magnetic load and has a low electric conductivity, only a repulsive force is generated in the load 15. However, since the load 15 has a low electric conductivity, the input power of about 2 kW is generated from the heating coil 16. Since the repulsive force due to the magnetic field generated is sufficiently small and the mass of the load 15 is large, the problem of load vibration does not occur. Therefore, by increasing the input power of the load 15 on the side of the heating unit 18 that does not include the smoothing means 13, it is possible to reduce the harmonic current and the load vibration.

In the case of the present embodiment, when the load 15 is a non-magnetic load and has high electrical conductivity, the input power in the heating section 18 is 0 kW (that is, heating is not performed by load detection), and the heating section 17 is heated. Input power is 1.
It is set to 6kW. The shape of the load 15 in this case also substantially covers the heating coil 16 as shown in FIG.
Furthermore, the thickness of the portion facing the heating coil 16 is approximately 1 m.
m or more.

When the load 15 is a non-magnetic load and has a low electric conductivity, a large repulsive force is generated in the load 15, and as a result,
A loud growling noise is produced. Therefore, the smoothing means 1
Heating is not performed in the heating section 18 not provided with No. 3, but heating is performed in the heating section 17 provided with the smoothing means 13. Further, since the maximum output at this time is made smaller than that at the time of heating the iron load, it is possible to realize an induction heating device in which load vibration is small and harmonic current is also small.

In this embodiment, as shown in FIG. 5, the temperature detecting means 20 (specifically, a thermistor is used).
The heating unit 17 has a function of detecting the temperature of the load 15 and controlling the electric power at the set temperature. Since the heating unit 17 has the smoothing means 13, the load 15 is less likely to vibrate, and as a result, temperature detection by heat conduction can be performed with high accuracy. Furthermore, since the heating unit has a smaller maximum output, the delay with respect to the temperature rise of the load 15 at the time of the maximum output can be small, and highly accurate temperature detection can be performed.

In this embodiment, non-magnetic stainless steel or aluminum having a thickness of approximately 1 mm or more is used, but for example, the first layer is a very thin non-magnetic stainless steel having a thickness of several hundred μm and the second layer is a multi-layer such as aluminum having a thickness of 2 mm. The load configuration of may be. In this case, since magnetic flux passes through the first layer of non-magnetic stainless steel, it is substantially the same as the material of aluminum.

The power factor improving means 12 may have a boost chopper structure as shown in FIG. In the case of the step-up chopper configuration, the chopper operation allows current to be supplied to the smoothing means 13 even when the commercial power supply 10 has a small voltage, and as a result, the power factor can be further improved.

[0035]

As described above, according to the invention described in claims 1 to 9, it is possible to realize an induction heating apparatus capable of simultaneously reducing load vibration and harmonic current.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an induction heating device according to an embodiment of the present invention.

FIG. 2 is a plan view of the induction heating device.

FIG. 3 (a) is a diagram showing a time change of an inverter supply voltage in a heating unit not including a smoothing unit, and (b) is a diagram showing a time change of an inverter supply voltage in a heating unit provided with a smoothing unit.

FIG. 4 is a circuit diagram of an induction heating device according to another embodiment of the present invention.

FIG. 5A is a sectional view showing a relationship between a heating coil and a load in the embodiment of the present invention, and FIG.

FIG. 6 is a circuit diagram of a conventional induction heating device.

FIG. 7 is a diagram showing a time change of the inverter supply voltage.

[Explanation of symbols]

10 Commercial power supply 13 Smoothing means 14 Inverter 15 load 16 heating coil 17, 18, 19 Heating part 20 Temperature detection means

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takahiro Miyauchi             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Yuji Fujii             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Akira Kataoka             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 3K051 AA02 AA03 AA08 AB04 AB08                       AC17 AC18 AC33 AC40 BD24                       CD14 CD33 CD35                 3K059 AA08 AB27 AB28 AC33 AD07                       AD23 CD19

Claims (9)

[Claims] 1. A maximum output of a heating unit having at least one heating unit equipped with an inverter power supply smoothing unit and at least one heating unit not equipped with an inverter power supply smoothing unit, and having an inverter power supply smoothing unit. Is smaller than the maximum output of the heating unit equipped with the smoothing means for the inverter power supply. 2. The input power at the time of heating a non-magnetic material load having a low electric conductivity in the heating section provided with the smoothing means is set smaller than the input power at the time of heating the load of the heating section not provided with the smoothing means. The induction heating device according to claim 1, wherein: 3. The induction heating device according to claim 2, wherein the non-magnetic material load is non-magnetic stainless steel. 4. The input power when heating a non-magnetic material load having a high electric conductivity in a heating section provided with a smoothing means is made larger than the input power when heating the load of a heating section not provided with a smoothing means. The induction heating device according to claim 1, wherein: 5. The induction heating device according to claim 2, wherein the thickness of the portion of the load facing the heating portion is set to approximately 1 mm or more. 6. The induction heating device according to claim 2, wherein the size of the load is set to substantially cover the heating portion. 7. The induction heating device according to claim 4, wherein the non-magnetic material load is an aluminum material load. 8. The induction heating apparatus according to claim 4, wherein the non-magnetic material load is an aluminum material or a copper material, and the input power of the copper material is smaller than that of the aluminum material. 9. The heating unit having a smoothing unit is provided with a function of controlling the load to a set temperature based on the temperature detection of the load by the temperature detecting unit. Induction heating device according to.